5F2A Circuit in a Harmony Combo Amp

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harmony004.jpg Board layout is backwards because the open end of the Harmony Chassis is front facing.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harmony001.jpg Tube holes have been enlarged to fit bigger tubes. Cutout for Power Transformer 022772.

This Harmony amp was direct drive - 110v or so with no power transformer. These can shock the user if the death cap fails. The only safe way to operate these old amps is to use an isolation transformer. This amp was in such poor condition that I decided to gut it and upgrade all components. There's lots of room inside. Easy to work on.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harmony002.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harmony006.jpg Select 25uF for boost or 1uF bypass cap. Resistor goes straight to ground. Bypass Caps are switchable. Blue wires go to SPDT toggle switch which grounds one cap or the other.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/Harmony007.jpg Preamp input grounds terminate here. Switch has two 1M resistors on it. See the Weber Maggie Amp Kit for details on the Boost Design which I boosted.

Cool build, I was looking at doing a Weber Maggie before I got into the Silvertones

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony1004.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony1006.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony1007.jpg Since this board is reversed, I wired the two sides of the twin triode preamp socket accordingly to minimize wire runs. For example, Pin 2 grid is where the input signal line in would normally go. Instead, I put the vol pot wiper on pin 2 which normally goes on pin 7. On pin 7 grid, I put the signal input. Each side has it's respective plate connection and cathode bias connection.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony1008.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2002.jpg
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2004.jpg
Detail of power side grounds. Green wire from first and second filter caps, Power Transformer Center Tap, Power Cord Ground, and if there be a heater center tap it would go here also. There be no heater center tap. Instead note 100 ohm resistors on pilot light and yellow wire to pin 8 on power tube.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2006.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2008.jpg
SPDT switch enables switching from 8 ohms to four ohms. Green wire is 4ohms, Yellow wire is 8 ohms. red wire from center of switch to hot tab on jack.

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2009.jpg

http://img252.imageshack.us/img252/7613/26478583.jpg
By boothillamps (http://profile.imageshack.us/user/boothillamps) at 2012-04-23

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/harmony2001.jpg

http://i1016.photobucket.com/albums/af283/haircuttingcowboy/5F16612002.jpg
http://i1016.photobucket.com/albums/af283/haircuttingcowboy/5F16612003.jpg
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http://i1016.photobucket.com/albums/af283/haircuttingcowboy/5F16612012.jpg

Nice one, how does it sound?

Sounds like a Champ. Seriously, Sounds great. Love it. With some creativity, you could put a Champ Circuit in about anything.

(That might make a good contest).

I've been sending some kits down your way. Australians are my number one off-shore customers.